The brothers’ task on “Skyline” is perhaps more daunting: proving themselves as full-fledged independent filmmakers.

Visual effects designers occasionally graduate into directing jobs — Eric Brevig (“Journey to the Center of the Earth”) and Stefen Fangmeier (“Eragon”) are two recent examples. But the 35-year-old Greg and the 33-year-old Colin aren’t just migrating from sitting at computer workstations to standing behind cameras. The pair also developed and financed the $10-million “Skyline” themselves, eventually selling it to Relativity Media, whose Rogue Pictures will release the alien attack drama on Friday.

“Skyline” unfolds in and around Marina del Rey, Calif., when a group of young adults awakens in an apartment (Greg’s own residence) to discover that Los Angeles is being ransacked by some unfriendly intergalactic visitors. Using a massive, seductive blue light beam, the interlopers suck up countless thousands of locals into their hovering spaceships, where worse things await.

Led by Jarrod (Eric Balfour), the group of thirtysomethings in the apartment scramble for cover, watching as the U.S. military struggles to drive out the invaders.

The dialogue in the screenplay by Joshua Cordes (who has worked as an animation supervisor for the brothers) and Liam O’Donnell (a visual effects consultant) is unlikely to attract much critical praise. Typical lines include “Oh my God!” “I can’t believe this!” “It just doesn’t seem real!” “Oh my God, oh my God!” and “Like it or not, this is happening!” (The film is not being shown early to film reviewers.)

But given the film’s limited budget and a quick 42 days of principal photography, audiences (and more than a few studio executives) should be impressed by “Skyline’s” elaborate visual tricks, some 900 effects shots that include rocket-firing stealth fighters, crashing helicopters, a nuclear explosion and aliens that look like flying metallic squids.

The film is not the first time the Brothers Strause, as they officially are credited, have directed together. They also made “AVPR: Aliens vs. Predator — Requiem” for 20th Century Fox three years ago, but say they did not enjoy the process, which required them to yield creative control to the studio, or the outcome. The $40-million movie grossed nearly $130 million worldwide, but was trashed by critics. “We were in directors’ jail,” Greg says. “So we had to do our own jailbreak.”

With visual effects jobs increasingly being shipped to countries such as India, the prices dropping for minor special effects work such as wire removal, and several U.S. companies closing their doors, the brothers decided it was exactly the right time to transform Hydraulx, as their effects shop is known, into a mini-studio.

So they bought camera and lighting equipment and built an editing suite. Now, they own pretty much everything necessary to make a movie except a catering truck and a costume shop.

The brothers say they were partially inspired to become filmmakers by some of the many directors they met doing visual effects. “We get to work with the bad and the good,” Greg says. “We work on a dozen movies a year, and you sometimes say, ‘How is this guy in the business?’”

At the same time, the brothers have not given up serving as an effects vendor for other filmmakers. On a recent afternoon in Hydraulx’s Santa Monica offices, several people were working on shots for the upcoming “Gulliver’s Travels” for 20th Century Fox and “Battle: Los Angeles,” the latter film sparking a minor squabble with Sony Pictures because its story is similar to “Skyline.”

“There are reasons to keep both businesses going,” Greg says. “But there are advantages to doing our own stuff.”

As young teens growing up outside Chicago, the brothers were obsessed with creating homemade visual effects. When their father was laid off from his repair job at IBM, he gave Colin and Greg his severance so they could buy a $20,000 Silicon Graphics workstation. It turned out to be a good investment.

“I think our first job was for like $80,” Greg says of creating a flying logo for a used car lot’s TV commercial. But soon thereafter, they ginned up a simulated bus washer for an industrial film and pocketed $10,000. They headed to Southern California soon thereafter. (Their mother became their accountant, and remains so to this day).

In 1996, they had visual effects credits on three movies: “The Nutty Professor,” “Black Sheep” and “The Stupids.” Their breakthrough came a year later: James Cameron asked the brothers to design a few shots of an iceberg for “Titanic.” The brothers unplugged the stove and the refrigerator in their Pacific Palisades apartment so the circuits wouldn’t blow when they powered up their computers. Working with Cameron wasn’t easy — the director would “videotape himself yelling at us,” Colin says, and then send the brothers his taped rants — but when “Titanic” came out, the visual effects jobs came pouring in.

In addition to working on features such as “Terminator 3: Rise of the Machines,” “Avatar,” “The Day After Tomorrow,” “X-Men: The Last Stand,” “2012” and “Fast & Furious,” the brothers have credits on a number of music videos, including effects-heavy productions for Tool, Usher and 50 Cent. But what they really wanted to do was to direct another feature, and realized they might have to bankroll it themselves. “We were hearing from all of our friends how impossible it was to get movies made,” Colin says.

The brothers initially considered improvising “Skyline’s” dialogue and making the film for $50,000. But after they shot a teaser trailer less than a year ago to spark some early pre-sales (well before “Skyline” was made), their ambitions grew.

They didn’t have the money to pay their crew of about 20 people, raising the funds through loans and investors. What’s more, they had to sell skeptical actors and agents on the project, where the compensation was deferred. “It wasn’t easy,” Greg says. “We were telling everybody, ‘You’re going to make zero. And we’ve never done this before.’” When shooting at Greg’s apartment complex garage, they would have to stop between takes so the parking attendant could retrieve residents’ cars.

With only themselves to please and no studio notes, “Skyline” was conceived, written, shot, edited and released in less than a year. “It’s been the least stressful thing we’ve ever done,” Greg says.

While they await “Skyline’s” release, the brothers are developing at least three other effects-driven movies, including a “Skyline” sequel. But as their slate grows, so do their needs for outside backers, and the potential for the same kind of creative interference they are trying to avoid.

“The most important thing for us is that we have to own the negative,” Colin says. “We don’t want to bring in a lot of investors, and then be asking for permission to do anything.”